[PhilJ]

Hi Peggy, I expect you meant the main XML sitemap, not the images XML sitemap.

You can edit the array of items that get outputted to the sitemap in /modules/XML_Sitemap/config.php

    3 => array(
        'type'           => 'S',
        'items_function' => 'xmlmap_get_pages',
        'properties'     => array(
            'lastmod'    => '',
            'changefreq' => 'never',
            'priority'   => '0.2',
        ),
    ),